1. Field
Example aspects of the present invention generally relate to an image forming apparatus, for example a copier, a printer, a facsimile and a multifunctional machine; and more particularly relate to an image forming apparatus including a fixing apparatus.
2. Discussion of the Background
Conventionally, in a fixing apparatus of an image forming apparatus such as a copier, a printer and the like, a nip portion is formed by abutting a fixing member, for example, a fixing roller, a fixing belt and a heat-resistant film against a pressure member, for example a pressure roller, a pressure belt and a heat-resistant film.
A recording medium is transported to the nip portion so that a toner image on the recording medium is fixed. Such a fixing apparatus has been widely used.
In such a fixing apparatus, it has been known that toner may electrostatically adhere to the surface of the fixing member. This phenomenon is so-called an electrostatic offset.
The electrostatic offset is a state in which toner or the toner image carried on the recording medium before a fixing process is electrostatically attracted to the surface of the fixing member.
The degree of attraction of toner or the toner image depends largely on the surface characteristics of the fixing member.
When the electrostatic offset is generated, the toner image adhered to the fixing member may be retransferred onto the recording medium after the fixing member rotates once. Consequently, a residual image may be formed.
Furthermore, the toner image adhered on the surface of the fixing member may be fixed to the fixing member each time the fixing member rotates. Consequently, a fixing failure may occur each time the fixing member rotates.
The problem described above, for example, has become a substantive problem for the image forming apparatus using oil-less toner of which demand has been increased recently.
In other words, in the image forming apparatus or the fixing apparatus using the oil-less toner a release agent is not necessarily applied on the surface of the fixing member. Consequently, the electrostatic offset may easily occur.
According to one related art, in order to suppress generation of the electrostatic offset by securing releaseability with a minimum amount of release agent, a narrow groove is provided in the fixing member, for example, a fixing belt in parallel with a sheet conveyance direction.
In one related art, in order to suppress gloss unevenness in an image, a material and a thickness of a surface layer of the fixing member are defined. The surface roughness (Rz) of the fixing member is formed to be no more than 1 μm, and the surface smoothness is optimized.
In one related art, in order to prevent contamination of the fixing member, ways in which the wettability of inorganic particulate contained in toner is optimized are proposed.
In one related art, in order to enhance the releasability of toner on the surface of the fixing member, a filler having affinity relative to the release agent is included in the fluoroethylene resin of the surface of the fixing member.
In one related art, in order to enhance the releasability of toner on the surface of the fixing member, fine asperities are formed on the fluoride polymer surface of the fixing member by way of sputter etching.
Furthermore, according to a related art, in order to prevent contamination of the fixing member, ways in which a surface tension (measured by a method disclosed in Japanese Industrial Standard K6768, the entire content of which are hereby incorporated herein by reference) of the fluoride polymer surface layer is in a range between 25 and 50 dyne/cm are proposed.
However, in the above-described related arts, it has been difficult to suppress the electrostatic offset with a relatively simple structure. When using the oil-less toner, the electrostatic offset has become a substantive problem.
Specifically, when providing a small groove in the fixing member, it takes time and is costly to manufacture the fixing member.
When the silicone oil serving as a release agent is applied on the surface of the fixing member, a desirable wettability may be achieved. Accordingly, gloss unevenness may be prevented.
On the other hand, when using the oil-less toner, the release agent is not applied on the surface layer of the fixing member. Consequently, the effect may be insufficient.
Furthermore, even if the surface roughness (Rz) of the fixing member is optimized, the electrostatic offset may not completely be suppressed.
In the above described related art, even if the wettability of the inorganic particulate in toner is defined, it may not be applicable to all kinds toner. Thus, a desirable releasability and durability may not be secured relative to all apparatuses.
In the above described related art, a desirable wettability may be achieved by using the silicone oil serving as a release agent applied on the surface layer of the fixing member. Accordingly, the releasability of toner of the fixing member may be enhanced.
However, when using the oil-less toner, the release agent is not applied to the surface layer of the fixing member. Consequently, a sufficient effect may not be achieved.
In the above described related art, toner may be adhered to the fine asperities formed on the fixing member.
Furthermore, in the above described related art, a desirable wettability may be achieved by using the silicone oil serving as a release agent applied on the surface layer of the fixing member so that contamination of the fixing member may be prevented.
However, when using the oil-less toner, the release agent is not applied to the surface layer of the fixing member. Consequently, a sufficient effect may not be achieved.